This application is based on Japanese Patent Application HEI 11-98626, filed on Apr. 6, 1999, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a reflecting mirror manufacture method and a lamp assembly, and more particularly to a method of manufacturing a reflecting mirror for reflecting light radiated from a light source to desired directions and illuminating a front space, and to a lamp assembly using such a reflecting mirror.
b) Description of the Related Art
For designing the light distribution of a vehicle front lamp, it is essential not only to form a predetermined light distribution but also to realize a sufficient illuminance in the central area of the front space and uniform diffusion of light in a horizontal direction. These requirements can be met generally by disposing a front lens and by controlling the reflection or the refraction direction of light radiated from a light source by changing the topological shape of a reflecting mirror surface.
The recent main trend of vehicle front lamps is to obtain desired light distribution characteristics only from the functions of a reflecting mirror surface. In this case, it is necessary to design the topological shape of a reflecting mirror surface so as to satisfy all light distribution requirements such as a central area illuminance and light diffusion.
An invention which obtains desired light distribution characteristics from the functions of a reflecting mirror surface is disclosed in the publication of JP-A-62-193002. According to this invention, desired light distribution characteristics are obtained by a composite reflecting surface formed by disposing in a horizontal direction a plurality of reflecting areas each having a vertically long rectangular shape with a vertical cross section of a parabola and a horizontal cross section of a particular curve. Since each reflecting surface of the vertically long rectangular shape has a parabola plane of a different shape, definite borderlines appear between the reflecting surfaces.
A lamp assembly using such a reflecting mirror has a variation in illuminance caused by the borderlines even if each reflecting surface is designed to have desired light distribution characteristics. Light reflected from a borderline becomes glare illumination light. Drivers of the vehicle and a vehicle running on the opposite lane may feel uncomfortable.
Another approach has been used in some cases in order to improve the uniformity and the like of light distribution characteristics. With this approach, a reflecting mirror is divided into a number of reflecting areas, and the topological shape of a reflecting surface is designed by taking into consideration the light distribution characteristics of each reflecting area. A composite reflecting mirror has been proposed and used in practice, this mirror having not only a rotary parabola plane but also a parabola column plane and the like, as the topological shape of each reflecting area (e.g., JP-A4-253101 and JP-A-9-306220).
The above-described reflecting mirrors are all a composite reflecting mirror having a reflecting surface made of a set of different parabola planes. Therefore, a definite borderline appears at the junction between respective reflecting areas, and in some cases steps are formed along these borderlines. These reflecting mirrors are, therefore, essentially associated with the problem of glare light.
An invention of a reflecting mirror satisfying light distribution characteristics necessary for vehicle lamp assemblies and having a continuous curved plane other than a parabola as the horizontal cross sectional shape, is disclosed in the publication of JP-A-9-82106.
The design method for the topological shape of a reflecting surface of a reflecting mirror disclosed in the publication of JP-A-9-82106 will be described briefly. First, a reference curve is determined which has a parabolic curve segment and an elliptic curve segment alternately disposed along a direction departing from the optical axis in the horizontal plane. In this case, the reference curve is determined so that an angle between the optical axis and a light beam reflected from each curve segment of the reference curve becomes larger as the curve segment is nearer to the optical axis.
Consider now a virtual rotary parabola plane having an axis, which is parallel to a vector of a light beam emitted from a light source and reflected at an arbitrary point on the reference curve and passes through the reflection point, and a focal point at a position of the light source. A reflecting surface is constituted of a set of cross lines between the rotary parabola plane and a vertical plane including the light beam vector.
A light beam image having a large projection area and formed by light beams reflected in an area near the center of the reflecting surface, is diffused largely in the horizontal direction. It is therefore possible to establish a sufficient vertical width of an area of a light distribution pattern near the opposite ends in the horizontal direction. A light source image having a small projection area and formed by an area near the peripheral area of the reflecting surface is controlled to contribute to the formation of the central area of the light distribution pattern. It is therefore possible to compensate for an insufficient illuminance caused by the lamp inserting hole in the reflecting surface.
If a front lens disposed in front of the reflecting mirror has almost no function of changing the refraction direction, the shape of the reflecting mirror can be seen directly via the front lens. The definite borderlines are therefore seen, which may be improper from the viewpoint of product design. When the reflecting mirror is used as a vehicle lamp assembly, the size and design are restricted depending upon the vehicle shape. While both these restrictions and light distribution characteristics are to be satisfied, it is difficult to design the reflecting mirror whose borderlines are not seen clearly.
For example, in the case of the composite reflecting mirror made of a set of a number of parabola plane reflecting areas and allowing steps to be formed at junctions between reflecting areas, it is possible to design the topological shape of the reflecting surface while the light distribution characteristics of each reflecting area is taken into consideration. Therefore, even if there is a change in the height of the reflecting mirror or the like because of restrictions on design or the like, design can be performed again to obtain desired light distribution characteristics by taking into consideration mainly those reflecting areas to be changed. The work required for such change is relatively simple.
However, if a reflecting mirror is to be designed in order to prevent the clear borderlines from appearing on the reflecting surface, a change in a partial reflecting area affects the topological shape of adjacent reflecting areas. More specifically, each small reflecting area is designed by considering the reflection directions at the border lines with adjacent reflecting areas and by satisfying the conditions of simulating the reflection directions and making small the deflection angle of a tangent line of the reflecting surface. This work is required to perform three-dimensionally. A change in the topological shape of one reflecting area results in a change in the topological shapes of adjacent reflecting areas. Such a change in the topological shape occurs in succession. Namely, the topological shapes of all areas of the reflecting surface are changed and the light distribution characteristics change. In order to design a reflecting mirror satisfying both the light distribution characteristics and design restrictions, a number of design works is required on the try-and-cut basis, resulting in a very long time and a large amount of man power.
If a reflecting surface of a lamp assembly particularly for opposite vehicle lane beams is to be designed, it is necessary to define a cut-off light distribution on the screen in order not to illuminate light in an area higher than a certain height. With a conventional design method, the topological shapes of a number of reflecting areas are designed so as to satisfy the cut-off light distribution of each reflecting area. In this case, the area on the screen illuminated with light beams reflected from the reflecting mirror is curved to have a banana shape with a lowered central area.
This essentially results from that the topological shape of the reflecting mirror is formed by a basic unit of the parabola reflecting plane shape and sharp cut-off characteristics are difficult to be obtained. With the lamp assembly having the banana-shaped light distribution characteristics, the right and left raised portions are improper because they become blinding light to opposing vehicles. In order to align the reflected image of a light source with the cut-off line, it is necessary to design the reflected image of the light source for each reflecting area and couple those reflected images. This process is very complicated and takes a long time. For example, if a reflecting mirror has a composite reflecting surface made of about 100 reflecting areas, one computer simulation for fine adjustment of the topological shape of each reflecting area to smoothly coupling the reflecting areas takes about 10 hours.
In view of the above-described circumstances, a reflecting mirror capable of realizing the light distribution characteristics with a high degree of design freedom has been long desired.
It is an object of the present invention to provide a reflecting mirror manufacture method and a lamp assembly suitable for obtaining desired light distribution characteristics.
According to one aspect of the present invention, there is provided a method of manufacturing a reflecting mirror for reflecting light radiated from a light source and illuminating a front space, comprising the steps of: defining light distribution characteristics for defining a correspondence relation between: a position of a reflection point on a cross line between a reference plane and a reflecting surface of the reflecting mirror whose topological shape is to be determined, the reference plane cutting the reflecting surface and a virtual screen set in front of the reflecting mirror; and a position of an image of the light source projected upon the virtual screen by light radiated from the light source and reflected at the reflection point, the light distribution characteristics providing a feature that the image of the light source formed by the light reflected at the reflection point has some width on the virtual screen in a direction crossing the reference plane when the reflection point is positioned in a first area in a direction along the cross line between the reference plane and the reflecting surface; determining in the reference plane a path line coincident with or approximate to the cross line between the reflecting surface and the reference plane, in accordance with the light distribution characteristics; determining a profile curve for each of a plurality of sampling points dispersibly distributed on the path line, in accordance with the light distribution characteristics, the profile curve passing through the sampling point, corresponding to the topological shape of the reflecting surface, and providing a feature that when the sampling point is positioned in the first area, as the reflection point moves along the profile curve, the image of the light source moves in the direction crossing the reference plane in accordance with the light distribution characteristics; and determining the topological shape of the reflecting surface in accordance with the profile curve determined for each sampling point.
According to another aspect of the present invention, there is provided a lamp assembly comprising: a light source; and a reflecting mirror for reflecting light radiated from the light source and illuminating a front space, wherein: in an x-y-z orthogonal coordinate system with a positive direction of a z-axis being set to a direction of the front space, a reflecting surface of the reflecting mirror is defined by an x-axis direction diffusion area, a y-axis direction rising area and a y-axis direction return area; in the x-axis direction diffusion area, as a reflection point moves in an x-axis direction, an illumination point also moves in the x-axis direction, and as the reflection point moves in a y-axis direction, a y-coordinate of the illumination point does not move; in the y-axis direction rising area, as the reflection point moves becoming remote from a z-x plane, the illumination point also moves becoming remote from the z-x plane; and in the y-axis direction return area, as the reflection point moves becoming remote from the z-x plane, the illumination point moves becoming near to the z-x plane.
A reflected light is diffused in one direction and can be diffused in another direction crossing the one direction. When the reflecting mirror manufacture method is applied to the reflecting mirror of a vehicle front lamp for crossing, the beam can be diffused from the horizontal direction to an upper oblique direction.